Bicycle Helmet Safety Institute

The Helmet Update

Volume 34, #6, November 27, 2016

Concussion helmets and jaw injuries

2016

Some thoughts on new trends in the concussion dialogue and a German study on helmets and jaw injuries.

What's new in concussion?

If you are looking for significant trends in the concussion dialogue, you can start with the realization that impacts cause injury, even if the injury is minor and not diagnosed. There is no "threshold of concussion." Mild traumatic brain injury is difficult to explain or predict from a given impact location, direction and severity. Rotational injuries occur from straight-on impacts. The brain models and impact sensors don't do a good job of predicting real-world injury. So even though most bicycle riders suffer fewer impacts than football players, they should probably still be concerned with how well their helmet performs in lesser impact scenarios. BMX or downhill mountain bike racing competitors who fall often should certainly be concerned. But no bike helmet standard is currently testing for low-velocity impact performance or for rotational force. Stay tuned.

German study claims hemets increase jaw injuries

A 2016 German study conducted at the Hannover Medical School has found:

"The use of bicycle helmets does not significantly reduce the incidence of mid-facial fractures, while being correlated with an even increased incidence of mandibular fractures."

The study was based on data on 5,350 crashes, with 537 wearing helmets (10%) and 4813 not wearing helmets. There were 18 jaw fractures, broken down as 5 with helmets (0.09%) and 13 without helmets (0.02%). So the authors concluded that helmets cause jaw injures. That seems like a stretch to us based on 5 crashes.

Their explanation grossly oversimplifies the crash scenario:
"At the time of crash the helmet hides first. Afterwards the unprotected mandible crashed because of the hyperflexion in the cervical spine." Annecdotal evidence indicates that the chin often hits before the helmet is even involved.

And finally, the authors acknowledge:
"The strongest limitation of our study was the small number of persons with helmet protection. So, the statistical analysis was vulnerable for coincidence and bias. We also had 911 cases (17%) with missing data of the speed and
did not know what kind of helmet was worn. Second, we were unaware of the exact location of the fractures. Therefore, it is difficult to separate the possible effect of the helmet on different fracture types. Furthermore, this fact hindered comparison of our data with those of other studies."

Our conclusion is that this study did not demonstrate what the authors said it did. Many other studies have found that bicycle helmets do offer some protection for the mid-face, but do not have an effect on jaw injuries. That seems to make more sense.